The combustion of fossil fuels contribute to air pollution. Gaseous compounds and other pollutants existing in flue gas are a result of the combustion of fuel containing such compounds. For example, the combustion of fossil fuels containing sulfur and organically-bound nitrogen and also from the combustion of air nitrogen produce emitted flue gas having sulfur-containing and nitrogen-containing compounds, in particular, oxides of sulfur (hereinafter “SOX”) and oxides of nitrogen (hereinafter “NOX”). For environmental and regulatory reasons, these pollutant compounds must be controlled to regulated levels in the flue gas before gas is allowed to be released to the environment.
Various methods of removing such compounds from a flue gas exist which provide various degrees efficacy, efficiency and cost. One method of removing compounds of sulfur are disclosed in U.S. Pat. No. 4,555,996, which issued on Dec. 3, 1985, and entitled “METHOD FOR REDUCTION OF SULFUR PRODUCTS IN THE EXHAUST GASES OF A COMBUSTION CHAMBER”. Another method of removing compounds of nitrogen are disclosed in U.S. Pat. No. 4,325,924, which issued on Apr. 20, 1982, and entitled “UREA REDUCTION OF NOX IN FUEL RICH COMBUSTION EFFLUENTS”. These methods contemplate introducing additives to the flue gas to reduce resultant pollution. There exists a need for more control of the introduction of additives in the flue gas.
One problem facing the removal of pollutants from a flue gas by injecting reactive sorbent into a chamber is the need for precise control over the temperature of the sorbent at the point of reaction with the pollutants. Injecting dry sorbent which reacts with SOX and NOX is problematic because the boiler chambers which produce these pollutants are extremely hot and cause the sorbent to partially melt and sinter before any effective removal can take place. This has led to using water to deliver the sorbent in the form of a water slurry.
It has been shown that injecting a slurry instead of a dry sorbent results in better performance. The slurry typically comprises a suspension of a sorbent within a liquid. By utilizing a slurry, the boiler heats up the suspension and boils off the liquid before it can melt the sorbent. By selecting an appropriate slurry mixture the sorbent is given additional time to travel towards the desired locations within the boiler before the liquid is all boiled off, thus preventing melting of the sorbent.
Nevertheless, it is still oftentimes difficult to deliver the appropriate amount of sorbent at the appropriate temperature to the appropriate locations in the boiler. Optimal pollutant-reduction reactions (i.e. sulftation, calcination and similar reactions) occur at certain thermal conditions. Many industrial boilers are designed with convective heat transfer surfaces located where these conditions occur. However, known injection methods cannot adequately deliver slurry into the boiler such that the right mixture of slurry is delivered to these locations where optimal reactions are able to occur, and cannot evenly distribute slurry into the main gas flow.
Another problem facing traditional pollutant removal practices is the amount of power needed to run the removal equipment, which can be quite expensive to operate. For instance, using scrubbers to reduce SOX and NOX emissions requires an expensive infrastructure. Additionally, the power needed to run such infrastructure is very large in comparison to the amount of power generated by the system. As such, traditional pollutant removal methods are parasitic in the sense that they consume a significant portion of the very power the system is meant to produce. Such a method of reducing SOX and NOX emissions using scrubbers causes the system to produce significantly more CO2 and greenhouse gas emissions due to its parasitic nature. Furthermore, these scrubbers are very expensive, take up a great deal of space and take a long time to assemble. What is needed is an apparatus and process for reduction of pollutants in combustion devices which does not require a high degree of parasitic power usage and has a relatively low cost.